Fix dry shrubs being placed in cacti and fix incorrect comments

mods/default/mapgen.lua

@@ -257,11 +257,11 @@ minetest.register_on_generated(function(minp, maxp, seed)
 			local z0 = minp.z + math.floor((divz+0)*divlen)
 			local x1 = minp.x + math.floor((divx+1)*divlen)
 			local z1 = minp.z + math.floor((divz+1)*divlen)
-			-- Determine cactus amount from perlin noise
-			local cactus_amount = math.floor(perlin1:get2d({x=x0, y=z0}) * 5 + 0)
-			-- Find random positions for cactus based on this random
+			-- Determine dry shrubs amount from perlin noise
+			local shrub_amount = math.floor(perlin1:get2d({x=x0, y=z0}) * 5 + 0)
+			-- Find random positions for dry shrubs based on this random
 			local pr = PseudoRandom(seed+1)
-			for i=0,cactus_amount do
+			for i=0,shrub_amount do
 				local x = pr:next(x0, x1)
 				local z = pr:next(z0, z1)
 				-- Find ground level (0...15)
@@ -272,9 +272,14 @@ minetest.register_on_generated(function(minp, maxp, seed)
 						break
 					end
 				end
-				-- If desert sand, make cactus
+				-- If desert sand, make dry shrub
 				if ground_y and minetest.env:get_node({x=x,y=ground_y,z=z}).name == "default:desert_sand" then
-					minetest.env:set_node({x=x,y=ground_y+1,z=z}, {name="default:dry_shrub"})
+					local p = {x=x,y=ground_y+1,z=z}
+					local nn = minetest.env:get_node(p).name
+					if minetest.registered_nodes[nn] and
+						minetest.registered_nodes[nn].buildable_to then
+						minetest.env:set_node(p, {name="default:dry_shrub"})
+					end
 				end
 			end
 		end